Approximately 6.8% of persons in the United States develop post-traumatic stress states, or as it is most commonly known PTSD, at some time in their lives. Experiences that most often give rise to PTSD include rape, assault, and combat; natural disasters or man-made accidents. More than 20 percent of the troops who fought in the Iraq and Afghanistan wars may be diagnosed with PTSD. PTSD is a condition that occurs following exposure to an extremely traumatic experience that results in an intense and prolonged response to stress. Most individuals who experience a traumatic event at some time during their lives will recover. A subset of individuals, however, develop PTSD. Biomarkers that diagnose and approximate PTSD risk would be of great value. Biomarker discovery in PTSD has been hindered by the lack of prospective studies in traumatized individuals.